Most vehicle drawn implements contain support wheels to raise or lower the implement with respect to the ground. In addition, some sort of fore-and-aft leveling means may be present to retain the implement parallel to the ground while it is being traversed over the ground.
In the past, an adjustable double-acting spring connection has been provided between the frame and the hitch structure of the implement to provide a means for varying the fore-and-aft weight distribution and also to accommodate a limited range of relative movement between the hitch and the frame. Such a construction is shown in U.S. Pat. No. 2,985,247, issued to W. P. Oehler et al. on May 23, 1961. A second method of leveling an implement relative to the ground included the use of a cylinder and spring arrangement as shown in U.S. Pat. No. 3,912,017, issued to Gary A. Rehn on Oct. 14, 1975. In the Rehn patent, mechanical adjusting means were provided wherein the operator would be required to leave the confinement of the vehicle and manually adjust the leveling mechanism on the implement by using hand tools. Furthermore, the lift wheels on the implement were attached to the frame by drop axles. In this design, a single hydraulic cylinder was used to activate all of the drop axles which were positioned horizontally on the elongated implement frame. The movement of the drop axles mechanically activated the raising or lowering of the lift wheels.
Neither of these methods or any other available leveling system provides on-the-go leveling features. Further, they require manual adjustment, necessitating the need for hand tools. This is particularly a frequent problem when an agricultural implement is used in fields having different soil conditions. Furthermore, the use of drop axles on the frame of a disk harrow creates a nuisance in that the debris of past crops and the newly turned over soil tends to cling onto the drop axles. This buildup of crop residue hinders the mechanical actuation of the drop axles and prevents the rotation of the disks themselves. Now an improved leveling system and control circuit has been invented which will eliminate these aforementioned problems.